This invention relates to a multi-cylinder internal combustion engine for controlling operation and the like of an intake valve and an exhaust valve disposed in an automobile engine and the like.
In general, in open/close control of an intake valve and an exhaust valve of an automobile engine, the open/close timing is set according to the operation condition obtained from an engine rotation speed, the amount of depression of an accelerator pedal, and the like. In such a valve-moving apparatus, there is proposed one which varies a cam profile according to the operating condition to improve the fuel consumption at a low speed and improve volumetric efficiency into the cylinder at a high speed. This is achieved by varying the open/close timing, lift amount, release time, and the like of the intake and exhaust valves at a low or a high speed.
Specifically, the automobile engine is provided with a high-speed cam and a low-speed cam, the high-speed cam having a cam profile which is able to obtain a valve open/close timing for high-speed operation, and on the other hand, the low-speed cam having a cam profile which is able to obtain a valve open/close timing for low-speed operation. During operation of the engine, the high-speed cam or the low-speed cam can be selectively used according to the operating condition to obtain an optimum open/close timing of the intake and exhaust valves.
Further, in such an automobile engine, there has been previously proposed a cylinder-closing mechanism which stops operation of two of four cylinders of a 4-cylinder engine to improve the fuel consumption. That is, in the valve-moving apparatus, during idle operation or low-load operation, the piston is operating but operation of the intake and exhaust valves is stopped to discontinue supply of fuel.
This cylinder-closing mechanism for stopping operation of the intake and exhaust valves is generally operated by providing a change-over mechanism in the rocker arm and hydraulically controlling the change-over mechanism. In this case, hydraulic pressure is supplied from a main oil pump of the engine to the change-over mechanism through an oil passage. However, a sufficiently high hydraulic pressure cannot be obtained from the main oil pump of the engine, for operating the change-over mechanism. Specifically, as shown in FIG. 13, there is a minimum required change-over hydraulic pressure necessary for operating the change-over mechanism, with the hydraulic pressure from the main oil pump of the engine being below the required change-over hydraulic pressure. Therefore, an assist pump is provided separately from the main oil pump of the engine to obtain a hydraulic pressure higher than the required hydraulic pressure.
FIG. 18 is a schematic plan view of a cylinder head showing the valve-moving apparatus for an engine having a prior art cylinder-closing mechanism, and FIG. 19 is a schematic view showing hydraulic pressure passages of the valve-moving apparatus.
As shown in FIGS. 18 and 19, a cam shaft 202 is mounted on a cylinder head 201 at its center, and a cam (not shown at a predetermined position) is integrally formed. A pair of rocker shafts 203 are also rotatably mounted to the cylinder head parallel to the cam shaft 202. Bases of a rocker arm 204 and a rocker arm 206 having a change-over mechanism 205 are individually mounted to the rocker shafts 203, and rocking ends of the individual rocker arms 204 and 206 are opposing top ends of intake or exhaust valve 207. An oil pump 208, an accumulator 209, and an oil control valve 210 are mounted at an end of the cylinder head 201. The oil pump 208 can be driven by a driving cam 211 mounted to one end of the cam shaft 202. The oil control valve 210 can be operated by a control signal from a control unit 212.
When the cam shaft 202 rotates, the rocker arm 204 and the rocker arm 206 are rocked by the cam to drive the intake and exhaust valves. Two of the four cylinders are unworked during idle operation or low-load operation of the engine. Specifically, the oil pump 208 is driven by the driving cam 211 of the cam shaft 202, and hydraulic pressure is stored in the accumulator 209. The control unit 212 judges operational condition of the engine according to signals from various sensors, and outputs a control signal to the oil control valve 210 to change over the valve. Then, hydraulic pressure is sent to the change-over mechanism 205 of the rocker arm 206, and operation of the corresponding intake and exhaust valves 207 is stopped. Therefore, the engine is operated merely by driving of the intake and exhaust valves 207 corresponding to the rocker arm 204.
In the above-described prior art valve-moving apparatus for an engine, some rocker arms 206 are provided with change-over mechanisms 205 to stop operation of two of the four cylinders during idle operation or low-load operation. For this purpose, the oil pump 208 or the accumulator 209 is required, and these must be mounted on the cylinder head 201. In the past, as described above, these devices have been provided on the top of one end of the cylinder head 201, but this causes part of the engine to protrude upward. And, a cylinder head cover which covers the upper portion of the cylinder head 201 must be formed so that part of it to be protruded upward accordingly, resulting in an increased height of the engine. This results in an increase in engine size, and difficulty in layout when the engine is mounted in a vehicle.
With a view to solving such problems, it is a primary object of the present invention to provide a multi-cylinder internal combustion engine which enables a compact internal combustion engine.